1. Field of the Invention
The present invention relates to a memory module, and more particularly, to a memory module having memory chips formed on a common substrate.
2. Description of the Related Art
Efforts have been ongoing to integrate different types of memories, such as dynamic random access memories (DRAMs), static random access memories (SRAMs) and/or flash memories, in parallel into a single memory module. See, for example, German patent publication DE 19626337A1, which suggests concurrent usage of chips containing volatile and nonvolatile memories.
Also, the so-called “Fusion Memory” has recently been suggested in which high density memory and logic circuits are integrated on a single chip. The memory circuits may include different types of memories on the single chip, such as DRAM, SRAM and flash memories. Attributes of the Fusion Memory may thus include the large storage capacity of a DRAM, the high speed data processing of an SRAM, and the nonvolatile storage of a flash memory. These attributes, coupled with on-chip logic circuits, allow for customization of the chip to meet desired specifications.
In the meantime, research has been conducted to fabricate a wafer-scale memory module in which a plurality of memory devices of the same type are formed and interconnected at the wafer level. See, for example, Japanese Patent Laid Open Publication No. 3-250662. According to this publication, in the event a defective device exists among the plurality of memory devices, a non-defective device is mounted on the defective device.
Wafer-scale memory modules are highly integrated and can be formed with smaller dimensions and lighter weights when compared with more conventional memory modules having memory chips mounted on a printed circuit board (PCB).
There exists a desire for a memory module which exhibits the attributes of wafer-scale technologies, while also allowing for a variety of memory functions to be integrated onto a common substrate.